1. Field of the Invention
The present invention relates to a recording and reproducing device that performs recording and reproduction on a hologram recording medium including a recording layer in which data is recorded by interference fringes between signal light and reference light and a reflection type circular polarization film formed under the recording layer and formed so as to output circularly polarized light in a same rotation direction as incident circularly polarized light as reflected light. The present invention also relates to a polarization direction controlling method in the recording and reproducing device.
The present invention also relates to a recording and reproducing device that performs recording and reproduction on a hologram recording medium including a recording layer in which data is recorded by interference fringes between signal light and reference light and a reflection type linear polarization film formed under the recording layer and formed so as to reflect only one of p-polarized light and s-polarized light.
2. Description of the Related Art
As described in Japanese Patent Laid-Open No. 2007-200385 (hereinafter referred to as Patent Document 1), for example, a hologram recording and reproducing system that records data by forming a hologram by interference fringes between signal light and reference light is known. In this hologram recording and reproducing system, at a time of recording, a hologram recording medium is irradiated with signal light that has undergone spatial light modulation (for example light intensity modulation) according to recording data and with reference light different from the signal light, and interference fringes (hologram) are formed on the recording medium, whereby the data is recorded.
At a time of reproduction, the recording medium is irradiated with reference light. When the recording medium is thus irradiated with the reference light, diffracted light corresponding to the interference fringes formed as described above is obtained. That is, a reproduced image (reproduced signal light) corresponding to the recording data is thereby obtained. The recording data is reproduced by detecting the thus obtained reproduced image by an image sensor such for example as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor.
FIG. 20 and FIGS. 21A and 21B are diagrams of assistance in explaining the hologram recording and reproducing system. FIG. 20 schematically shows a recording method. FIGS. 21A and 21B schematically show a reproducing method.
FIG. 20 and FIGS. 21A and 21B show a recording method and a reproducing method in a case where a so-called coaxial system, in which recording is performed with signal light and reference light arranged on an identical optical axis, is employed.
In addition, these figures illustrate a case of using a hologram recording medium 100 of a reflection type having a reflective film.
First, as shown in FIG. 20 and FIGS. 21A and 21B, in the hologram recording and reproducing system, an SLM (spatial light modulator) 101 is provided to generate signal light and reference light at a time of recording and reference light at a time of reproduction. The SLM 101 has an intensity modulator that subjects incident light to spatial light intensity modulation (referred to also as light intensity modulation or simply as intensity modulation) in pixel units. The intensity modulator can be formed by a liquid crystal panel, for example.
First, at the time of recording shown in FIG. 20, signal light given an intensity pattern corresponding to recording data by the intensity modulation of the SLM 101 and reference light given a predetermined intensity pattern are generated. The coaxial system subjects incident light to spatial light modulation such that the signal light and the reference light are arranged on an identical optical axis as shown in FIG. 20. At this time, in general, the signal light is disposed inside, and the reference light is disposed outside the signal light, as shown in FIG. 20.
The signal light and the reference light generated in the SLM 101 are applied to the hologram recording medium 100 via an objective lens 102. Thereby a hologram reflecting the recording data is formed by interference fringes between the signal light and the reference light on the hologram recording medium 100. That is, the data is recorded by the formation of the hologram.
At the time of reproduction, as shown in FIG. 21A, the SLM 101 generates reference light (the intensity pattern of the reference light at this time is the same as at the time of recording). Then, the hologram recording medium 100 is irradiated with the reference light via the objective lens 102.
In response to such irradiation of the hologram recording medium 100 with the reference light, as shown in FIG. 21B, diffracted light corresponding to the hologram formed on the hologram recording medium 100 is obtained, and thereby a reproduced image of the recorded data is obtained. In this case, the reproduced image is guided to an image sensor 103 via an objective lens 102 as shown in FIG. 21B as reflected light from the hologram recording medium 100.
The image sensor 103 receives the light of the reproduced image guided as described above in pixel units, and obtains an electric signal corresponding to an amount of received light for each pixel. The image sensor 103 thereby obtains a detected image for the reproduced image. The image signal thus detected in the image sensor 103 is a readout signal of the recorded data.
Incidentally, as is understood from the description with reference to FIG. 20 and FIGS. 21A and 21B, the hologram recording and reproducing system records/reproduces recording data in a unit of the signal light. That is, in the hologram recording and reproducing system, one hologram (referred to as a hologram page) formed by a one-time interference between the signal light and the reference light is a minimum unit of recording/reproduction.